The invention relates to a method for operating a refuse incineration plant. The method further relates to a regulating system for regulating at least one of the operating parameters of a refuse incineration plant, and to a refuse incineration plant having a regulating system of this type.
The operation and in particular the uniform generation of heat in oil-fired or coal-fired power plants does not cause problems. This uniform generation of heat is achieved by uniform metering of the fuel, the quality of which is constant and known. The main aim of refuse incineration plants too is to keep the heat output constant. In addition, the flue gas has to comply with certain statutory regulations with regard to quality and quantity. The heat output cannot be controlled simply by metering the refuse supplied, since the calorific value of the refuse, on account of its differing composition and the varying water content, may fluctuate considerably. Accordingly, it is already difficult to maintain a constant quantity of heat. Additional optimization of the other parameters causes even more problems.
EP-B-0 499 976 has disclosed a method for operating a refuse incineration plant in which, to make the amount of heat which is generated more uniform, the supply of refuse, i.e. the movement of the metering ram, the conveying of refuse on the grate, i.e. movement or lifting frequency of the grate parts, and the supply of primary air is regulated by means of a cascaded regulating system. The quantity of steam which is generated is recorded with a slight delay and is used as the main regulating variable. The value for the oxygen content of the flue gas, which is rapidly available, is used as an auxiliary regulating variable. With this firing capacity regulation, it is possible for the refuse incineration plant to be substantially automatically matched to slightly changing properties of refuse and therefore to minor fluctuations in calorific value. However, the grate frequency, ram movement and primary air supply are always increased or reduced in the same direction. Consequently, this fire capacity regulation does not sufficiently compensate for relatively substantial changes in the condition or calorific value of the refuse which require the operating parameters to be changed in opposite directions. This is the case, for example, when switching over to wet, highly compacted refuse, in which case the ram velocity should be lowered in order to reduce the supply of refuse and the grate frequency should be increased in order to split or break up the refuse. In the known process, although the fluctuation in calorific value is compensated for in the short term by fanning or retarding the firing intensity and in the longer term by means of the metered quantity of refuse, the automatic fire capacity regulation takes no account of the correct incineration profile over the grate length.
In practice, such changes in the calorific value are usually compensated for by an operator by visual assessment of the condition of the refuse or the state of the fire. The operator then manually adjusts individual operating parameters; for example, in the case of wet refuse, the primary air preheating is often increased. A problem of this is that it is complicated to adjust the operating parameters, on account of the wide range of possible actions and interactions, and the adjustments are not always selected optimally. Furthermore, success is very dependent on the experience of the operator. The regulating process has an extremely long delay time, and consequently the full effects of an intervention can only be assessed after about an hour.
Therefore, the invention is based on the object of simplifying operation of a refuse incineration plant, in particular of providing a method for operating a refuse incineration plant in which the operating parameters are to a large extent automatically adapted to changing refuse properties, in particular fluctuations in the calorific value.
To operate a refuse incineration plant, after the fire has been fanned, the generation of heat is made more uniform (fire capacity regulation) in a manner known per se by regulating a plurality of operating parameters, including at least one of the operating parameters: refuse metering; residence time on a grate and quantitative supply of primary air, as a function of a plurality of measured variables, including at least one of the measured variables: oxygen content in the flue gas and quantity of steam generated. By way of example, the method which is known from EP-B 0 499 976 is used. According to the invention, a calorific value parameter, which is a measure of the calorific value of the metered refuse or the change in this value, is derived from a measured variable. As a modification to the known control techniques, at least one of the operating parameters is adjusted at least in part as a function of the calorific value parameter.
The calorific value or the change in this value is automatically recorded by analyzing suitable measured variables. The calorific value parameter is used to influence the regulation of at least one operating parameter in accordance with a predetermined plan which is, for example, empirically determined or drawn up using model calculations. Ideally, therefore, no manual intervention is required, but rather the intervention takes place automatically on the basis of objective criteria, and the plant can in principle be left to run itself.
In addition, it is also possible to provide the option of manual intervention. To this end, the calorific value or the change in this value is estimated by an operator, for example by observing the fire position. The process control unit is used to input as calorific value parameter a variable which indicates, for example, the extent to which the estimated calorific value deviates from the nominal calorific value assumed when dimensioning the firing installation.
The measured variable for the calorific value parameter is recorded automatically. In an advantageous refinement of the method, the moisture content of the flue gas is used as a measure for the calorific value. This is based on the fact that the calorific value of the refuse is substantially determined by its water content. Since the water contained in the refuse begins to evaporate as soon as it is fed into the furnace, the measured moisture content reproduces changes in the refuse composition without a major time delay. A corresponding signal is then immediately available in order for the operating parameters or the regulation thereof to be matched to the changed calorific value. The moisture content of the flue gas can be measured directly by means of a humidity sensor. Preferably, however, the flue gas is saturated with water, and the readily measurable temperature of the saturated flue gas is used as a measure of the moisture content and therefore of the calorific value. The extraction of heat through evaporation is greater if less water was present in the flue gas from the outset. The temperature of the water-enriched flue gas is therefore a measure of the original water content of the refuse and therefore of the calorific value. Since in many refuse incineration plants a water injection means and a scrubber are present, this variant can be implemented particularly easily. The temperature is preferably measured downstream of the water injection means, in the sump of the scrubber or at the scrubber outlet.
The calorific value parameter is used to automatically determine at least one correction variable which modifies at least one of the setting values from the fire capacity regulation and/or one of the variables used for fire capacity regulation, e.g. input variables or amplifications of regulators involved. Preferably, a plurality of operating parameters are influenced in such a way, so that, by means of an intervention or on the basis of the automatically recorded calorific value, the characteristic diagram of the entire plant can be shifted and optimally matched to the changed calorific value. Correction variables are determined, for example, on the basis of model calculations or are based on empirical values.
The correction variable is used, for example, to shift the setting range or working point of an individual regulator, while the capacity regulation otherwise keeps the heat output constant in a known way.
In a further advantageous refinement of the invention, the correction variable determined from the calorific parameter value is used to modify the regulator amplification of at least one regulator. In this way, the operating range of this regulator is adapted to the changed calorific value. In addition, corresponding correction variables determined from the same calorific value parameter can also be used to adapt the setting value and/or the desired value of this regulator or of other regulators.
Preferably, the following operating parameters are adjusted as a function of the calorific value parameter: sum of primary air and secondary air, ratio of primary air to secondary air, zone flap position, primary air, refuse metering, residence time on the grate, desired oxygen value, primary air preheating.
The regulating system according to the invention for regulating at least one of the operating parameters of a refuse incineration plant has at least one regulator which, on the basis of at least one regulating variable supplied as an input signal and/or at least one desired value, generates an output signal which is fed as a setting value to one of the actuators for the ram, grate, primary air flaps or primary air preheater. According to the invention, there is a first measuring device for recording a measured variable from which a calorific value parameter, which is a measure of the calorific value of the refuse or the change in this value, is derived. Furthermore, there is a calorific value correction unit which, on the basis of the calorific value parameter, generates at least one correction variable, which is used to modify at least one desired value and/or setting value and/or a regulator amplification of the at least one regulator.
The regulating system is used in particular to carry out the method according to the invention.
A refuse incineration plant having a regulating system of this type has all the advantages of the regulating system.